The spine is critical in human physiology for mobility, support, and balance. The spine protects the nerves of the spinal cord, which convey commands from the brain to the rest of the body, and convey sensory information from the nerves below the neck to the brain. Even minor spinal injuries can be debilitating to the patient, and major spinal injuries can be catastrophic. The loss of the ability to bear weight or permit flexibility can immobilize the patient. Even in less severe cases, small irregularities in the spine can put pressure on the nerves connected to the spinal cord, causing devastating pain and loss of coordination.
Surgical procedures on the spine often include the immobilization of two or more vertebra. Immobilizing the vertebrae may be accomplished in many ways (e.g. fixation plates and pedicle screw systems). One of the most common methods for achieving the desired immobilization is through the application of bone anchors (most often introduced into the pedicles associated with the respective vertebra to be fixed) that are then connected by rigid rods locked to each pedicle screw. These pedicle screw systems are very effective. Pedicle screws generally include an anchor component and a rod-housing component (or “tulip”) that is often coupled to the anchor component in a manner that permits angular adjustability of the tulip relative to the anchor component in one or more planes. Once the pedicle screws are implanted in the desired positions a spinal rod is seated in each tulip and locked in position. The angular adjustability of the tulips is also locked, either through the locking of the rod, or independently thereof, to thus fix the connected vertebrae relative to each other. Pedicle screw configurations which allow increased angulation of the housing component in one direction are useful in certain situations where an increased pivot angle is needed (e.g. where there is an acute angle between the anchor component and rod trajectories, such as occurs, for example, with S2-Alar screws). However, configurations that permit the increased angulation also tend to reduce the strength of the connection between the anchor component and rod-housing component. Therefore a need exists for new and improved anchors with increased angulation housings but without the reduction in connection strength suffered in current solutions.